Our specific objective is to examine, both physiologically and anatomically, interneuronal synapses in tissue culture. We propose to determine some of the conditions necessary for synapse formation and to investigate the types of neurotransmitter receptor sites on the postsynaptic neuron during differentiation of synapses in vitro. Initially we will emphasize physiological studies of an established culture system consisting of dissociated superior cervical ganglion (SCG) neurons and spinal cord explants. Results from these studies will be compared with existing data on the superior cervical ganglion in vivo. Simultaneously, anatomical analyses will be undertaken in combined cultures in which SCG neurons will be presented with a variety of presynaptic neurons that have been selected because they release different neurotransmitters or normally make contact with neurons containing different types of postsynaptic receptors (i.e., muscarinic vs. nicotinic). Selected combination cultures, in which synapses are demonstrated anatomically, will subsequently be subjected to physiological investigation. In order to gain insight into the embryological events that determine the receptors present on the neuronal membrane, we will attempt to culture neurons taken from embryonic SCG prior to innervation and to determine, with intracellular physiological studies, which receptors are expressed under these conditions. BIBLIOGRAPHIC REFERENCES: Rees, R. P., Bunge, M. B. and Bunge, R. P. Morphological changes in the neuritic growth cone and target neuron during synaptic junction development in culture. J. Cell Biol., 68 (2), 240-263, 1976. Ko, C-P., Burton, H., Johnson, M. and Bunge, R. P. Synaptic transmission between rat superior cervical ganglion neurons in dissociated cell cultures. Brain Research. In press, 1976.